This invention relates to a fertilizer product and method utilizing nitrogen, potassium and phosphorous which are essential elements for plant growth. Fertilizers invariably contain one or more of these elements and those in frequent use at the present time include urea, ammonium nitrate, potassium chloride, sodium nitrate, monoammonium phosphate, potassium sulfate, calcium cyanamide, potassium nitrate, mixtures of calcium acid phosphate and calcium sulfate known as superphosphate, and the like. Urea is a preferred source of nitrogen because of its relatively high nitrogen content in the range of forty-seven percent by volume.
Although in some cases soil analysis shows that only nitrogen fertilizer is required and hence is applied solely, in the majority of cases all three of the aforementioned essential elements are needed. Accordingly the fertilizer actually applied to the soil is a blend of a nitrogen, potassium and phosphorous fertilizers with some compounds such as diammonium phosphate containing more than one essential element. It is conventional to state the amount of essential elements in a complete fertilizer by a series of numbers which refer, in sequential order to the weight percentage of nitrogen as N, phosphorous as P.sub.2 O.sub.5 and potassium as K.sub.2 O. For example a 10-10-10 fertilizer contains 10% nitrogen, 10% phosphorous, and 10% potassium by weight. Inert materials are provided with the fertilizer materials to maintain the percentage of the essential elements present in the fertilizer at a relatively low level. This is in an attempt to avoid excessive local concentrations of an essential element in the soil and which may result in a burned root growth.
The readily water soluble property of most fertilizers creates a number of disadvantages steming from the additional need of plants for watering. With watering much of the fertilizer may be dissolved in the water and soaked into the soil below the plant roots thereby never becoming available to the plants. Also there is the possibility that water applied to the plant may result in the disadvantage that the fertilizer becomes available to the plant too rapidly resulting in injury to the plant. This is often seen in burned plants.
The prior art has addressed itself to the aforementioned problem by the use of coatings for granular fertilizers and tableted or shaped forms of fertilizers made from largely water-insoluble components intended to disintegrate and regulate the release of fertilizer materials relatively slowly.
Tableted and coated fertilizers are not able to accomplish the purposes of the present invention. For example many tablets are too rapidly soluble with the result of too rapid leaching of the contained fertilizer particularly for container grown plants. On the other hand slowly soluble non-disintegrating tablets for use with trees, as shown in U.S. Pat. No. 3,024,098 may last a long time, up to two years. However, these tablets or shaped forms do not make a controlled amount of food available at the beginning; nor do they make it available thereafter at a controlled rate as required by container grown plants. This is because the tablets remain hard by not exposing surface areas to solubilization by moisture and bacterial activity. Bacterial activity is essential to the solubility of some of the main ingredients of plant food.
As concerns coated granular fertilizers, the general desire for delayed action by high-analysis fertilizer is well known and the prior art has conventionally addressed itself to this problem by the use of appropriate coatings for granular fertilizers. Granules of fertilizer are frequently non-uniform in composition and contain surface cracks and crevices thereby tending to pulverize readily. Accordingly the prior art has found considerable difficulty in obtaining a uniform and practical coating for granular fertilizers as related to the preparation of granular materials and the application of coatings therefor, the wide variety of uses are almost impossible to contemplate so that a particular coating and granular size is likely to provide undesirable results in some applications.
A further problem exists with presently known methods of supplying fertilizer in that even though a substantial supply of nutrient containing plant food is made available, the plant may not get its benefit. If the source of nutrients is highly soluable it may be leached out before the plant roots draw upon it. Also, there is the possibility that the plant food may revert to an insoluable form if left in the soil too long subjecting it to an excess of moisture and microbial activity. The potassium and phosphate plant foods in particular are susceptible to this conversion. For example, monocalcium phosphate may change to dicalcium phosphate or to aluminum or iron phosphates illustrating a reversion or fixation of phosphate in the soil in a form such that it is not available for the intended plants. As much as eighty percent of these foods may be rendered unavailable.
It is an object of this invention to provide a fertilizer product and a method which releases essential moisture and plant food to a plant without possibility of injury thereto. This is on a systematic basis essentially controlled by the needs of the plant as indicated by the plant itself.
It is an object of this invention to isolate a plant's root system from supplied food nutrients until actually required by the plant, to prevent possibility of plant root system damage from excessive exposure.
It is another object of this invention to make plant food nutrients available in soluble form to a plant at a rate empirically required by the plant, to prevent possibility of plant root system damage from excessive exposure.
It is yet another object of this invention to make plant food nutrients available in soluble form to a plant at a rate empirically related to the plant's needs and its growth rate.
It is a further object of this invention to provide means for systematic plant watering related to a plant's aspiration rate.
It is a further object of this invention to prevent highly water soluble nitrogeneous plant foods from being made unavailable for plant usage by indiscriminate watering.
It is another object of this invention to make plant food compositions of phosphorus and potassium substantially available as soluble forms of plant food.
Other further objects of this invention will become more readily apparent as the disclosed subject matter is more fully understood from the following disclosure.
The invention comprises the achievement of the aforesaid objects by essentially excluding plant food intended for plants from access thereto except by passage through osmotic membranes. These membranes are able to provide the function of osmosis, reverse osmosis, and microporosity cooperatively with forces of capillary pressure as it exists in porous soils in which plants are normally grown.
It is known that it is possible to carry out osmotic exchanges through membranes made of a water swellable microporous paper such as felted cellulose or membranes made of a water swellable polymer such as polyvinyl alcohol. Of course membranes composed of any material providing the osmotic exchange can be used in practicing the subject invention. Heretofore it has not been known to essentially totally exclude plant food from a plant when placed in the soil for release to the plant except by passage through the subject osmotic membranes.
The terminology "osmosis membrane" and "reverse osmosis membrane" has particular significance in pointing out and clearly defining the nature of the material which provides the encasement for the fertilizer materials of this invention. The nature of the material is such that when used as membrane material it is able to provide the function of osmosis in the presence of solute-solvent combinations; it provides the function of reverse osmosis under certain pressure gradient conditions; and provides the aforementioned microporosity necessary to these functions. These are, of course, entirely different functions from mechanically providing perforations in a material to permit liquid to drain through. In fact, the preferred microporosity is that able to effect macromolecular range particle separation from 10.sup.-4 to 10.sup.-7 millimeters.